While patients with chronic lymphocytic leukemia (CLL) respond to combined therapy with fludarabine and rituximab, patients relapse and eventually become refractory to treatment. Therefore, improving response to chemoimmunotherapy in CLL is a high priority, and there is great interest in novel therapeutic agents that may enhance this response. Rituximab induces apoptosis in CLL cells but concurrently generates an antagonizing cell survival signal by phosphorylating and activating AKT. Over-expression of TCL-1 in murine lymphocytes using a transgenic mouse model resulted in AKT activation and development of a murine leukemia similar to human CLL. TCL-1 is over-expressed in human CLL cells, providing an impetus for laboratory and clinical studies to target the reduction of TCL-1 and kinases such as AKT, which are influenced by TCL-1. The investigational drug 17-allylamino-17-demethoxygeldanamycin (17-AAG) depletes AKT by inhibiting the chaperone protein Hsp90, which normally protects AKT from proteosomal degradation. In preclinical studies in our laboratory, 17-AAG down-regulated AKT in CLL cells, and exposure of CLL cells to rituximab and 17-AAG resulted in greater apoptosis than that achieved by either agent alone. Specific Aim 1 of this grant is to perform a phase I dose escalation study of 17-AAG, combined with fludarabine and rituximab, in patients with fludarabine-refractory CLL, in order to determine the maximum tolerated dose (MTD), toxicity profile and preliminary clinical activity of 17-AAG as a single agent and in combination therapy. Specific Aim 2 is to examine the pharmacokinetics of 17-AAG to determine the relationship of pharmacokinetic parameters such as Cmax, Css and AUC to modulation of pharmacodynamic targets. Specifically, we will examine the effects of 17-AAG on the PDK1/AKT/TCL-1 pathway and other proteins dependent upon Hsp90 binding. In addition, we will examine whether 17-AAG affects spontaneous, drug-induced and rituximab-induced apoptosis, and whether concurrent administration of fludarabine and rituximab increases the apoptotic response to 17-AAG as a single agent. [unreadable] [unreadable]